1. Field of the Invention
One or more embodiments of the present invention relate to a cylindrical secondary battery, and more particularly, to a cylindrical secondary battery including a center pin having an improved structure.
2. Description of the Related Art
Secondary batteries are rechargeable batteries, which are widely used in portable electronic devices such as mobile phones, notebook computers, camcorders, etc. According to their shape, the secondary batteries are classified into cylindrical, square, pouch-shaped batteries, and the like.
A cylindrical secondary battery includes an electrode assembly formed by winding a stack of an anode plate, a cathode plate, and a separator disposed between the anode and cathode plates in a jelly roll shape. The electrode assembly is inserted through an opening of a cylindrical case into the cylindrical case, and a cap assembly seals the opening.
At this point, a center pin is inserted into a central opening of the electrode assembly to maintain the jelly roll shape. Also, the center pin is inserted into a lower end portion to press a cathode plate tab connected to the cathode plate and to make the cathode plate tab contact the cylindrical case. Accordingly, the center pin and the cylindrical case are stuck together and the jelly roll is tightly maintained by inserting the electrode assembly into the cylindrical case and inserting the center pin into the central opening of the electrode assembly.
In general, the center pin is a cylindrical member having a diameter slightly smaller than a diameter of the central opening of an electrode assembly. For example, when the electrode assembly has a central opening with a diameter of 3 mm, a cylindrical center pin with a diameter of about 2 mm is inserted into the central opening of the electrode assembly to perform the above-mentioned function. However, in this case, even though the center pin is easily inserted into the central opening, noise is generated due to collision of the center pin with the electrode assembly when a product including the cylindrical secondary battery is shaken. That is, since the central opening is larger than the center pin, a space is formed between the center pin and the electrode assembly, and the center pin is shaken when the secondary battery is moved. As the center pin moves inside the central opening, the center pin collides with a side wall of the electrode assembly surrounding the central opening, thereby generating noise. Such noise may affect the reliability of the product, and thus, a center pin not generating noise is required.